Viterbi Decoder Alternate-Path Correction After CRC Failure
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Solution Overview
Problem
Current Viterbi decoders face challenges in efficiently decoding convolutionally encoded data with high error rates, particularly in identifying the most likely path through a trellis diagram and correcting errors in a communication system, which can lead to incorrect data reception.
Innovation Solution
The proposed error correcting Viterbi decoder employs a Viterbi algorithm that computes the most likely sequence of channel symbols, performs error checks, and identifies merge points to find alternate paths that pass error checks, using a combination of de-interleaving, de-puncturing, and cyclic redundancy checks to ensure accurate data decoding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Viterbi decoder uses the standard Viterbi algorithm to decode convolutionally encoded data, then it can identify the most likely path through the trellis diagram, but it fails to correct errors when the most likely path contains decoding errors
Solution Approach 1:
The patent performs preliminary error detection using CRC check before finalizing the decoding result. After the Viterbi algorithm identifies the most likely path, the system proactively checks for errors using cyclic redundancy check on the decoded data. If errors are detected, the system prepares to perform corrective actions by examining alternative paths, thus preventing erroneous data from being output.
Solution Approach 2:
The patent implements a feedback mechanism where the CRC error detection result feeds back into the path selection process. When the CRC check fails on the most likely path, the system uses this feedback information to search for alternative paths in the trellis diagram, re-decode using those paths, and re-check for errors, creating a closed-loop error correction system.
2Reliability
If the Viterbi decoder examines multiple alternate paths to correct errors, then error correction capability improves, but computational complexity and decoding time increase
Solution Approach 1:
The patent applies partial action by examining only a limited number of alternate paths (e.g., second most likely, third most likely paths) rather than exhaustively searching all possible paths through the trellis diagram. This selective approach provides sufficient error correction capability for typical error rates while avoiding the exponential complexity increase that would result from examining all possible paths.
Solution Approach 2:
The system performs preliminary error detection using CRC check before committing to a decoding result. This preliminary action allows the system to determine whether alternative path examination is necessary, avoiding the computational overhead of examining multiple paths when the most likely path is already correct.
3Reliability
If the Viterbi decoder implements comprehensive error checking and alternate path analysis, then error correction capability improves, but processing time and computational resources increase
Solution Approach 1:
The patent implements partial action by performing error checking and alternate path analysis only when necessary - specifically, only when the CRC check on the most likely path fails. This conditional approach provides robust error correction capability while avoiding the time penalty of always examining multiple paths, thus resolving the contradiction between reliability and processing time.
Data Source
AI summary
Methods and corresponding systems in a Viterbi decoder include computing a maximum likelihood (ML) path in a Viterbi trellis in response to executing a first Viterbi algorithm. Thereafter, one or more merge points are selected on the ML path in a second Viterbi algorithm, wherein the merge points each have a path metric difference, which is a difference between an ML path metric at the merge point and a non-surviving path metric at the merge point. Merge points are selected based upon relative path metric differences associated with nodes on the ML path. Next, alternate paths in the Viterbi trellis are computed based on the ML path with alternate paths substituted at corresponding merge points. A passing decoded bit sequence is output in response to passing an error check, wherein the passing decoded bit sequence is associated with one of the one or more alternate paths.